.\" $NetBSD: nsswitch.conf.5,v 1.14 1999/03/17 20:19:47 garbled Exp $
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.\" by Luke Mewburn.
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.Dd September 6, 2020
.Dt NSSWITCH.CONF 5
.Os
.Sh NAME
.Nm nsswitch.conf
.Nd name-service switch configuration file
.Sh DESCRIPTION
The
.Nm
file specifies how the
.Xr nsdispatch 3
(name-service switch dispatcher) routines in the C library should operate.
.Pp
The configuration file controls how a process looks up various databases
containing information regarding hosts, users (passwords), groups, etc.
Each database comes from a source (such as local files, DNS, NIS ,
and cache), and the order to look up the sources is specified in
.Nm .
.Pp
Each entry in
.Nm
consists of a database name, and a space separated list of sources.
Each source can have an optional trailing criterion that determines
whether the next listed source is used, or the search terminates at
the current source.
Each criterion consists of one or more status codes, and actions to
take if that status code occurs.
.Ss Sources
The following sources are implemented as part of the base system:
.Pp
.Bl -tag -width Source -compact
.It Sy Source
.Sy Description
.It files
Local files, such as
.Pa /etc/hosts ,
and
.Pa /etc/passwd .
.It db
Local database.
.It dns
Internet Domain Name System.
.Dq hosts
and
.Sq networks
use
.Sy IN
class entries, all other databases use
.Sy HS
class (Hesiod) entries.
.It nis
NIS (formerly YP)
.It compat
support
.Sq +/-
in the
.Dq passwd
and
.Dq group
databases.
If this is present, it must be the only source for that entry.
.It cache
makes use of the
.Xr nscd 8
daemon.
.El
.Pp
Additional sources might be provided by third party software.
.Ss Databases
The following databases are used by the following C library functions:
.Pp
.Bl -tag -width networks -compact
.It Sy Database
.Sy "Used by"
.It group
.Xr getgrent 3 ,
.Xr getgrent_r 3 ,
.Xr getgrgid_r 3 ,
.Xr getgrnam_r 3 ,
.Xr setgrent 3 ,
.Xr endgrent 3
.It hosts
.Xr getaddrinfo 3 ,
.Xr gethostbyaddr 3 ,
.Xr gethostbyaddr_r 3 ,
.Xr gethostbyname 3 ,
.Xr gethostbyname2 3 ,
.Xr gethostbyname_r 3 ,
.Xr getipnodebyaddr 3 ,
.Xr getipnodebyname 3
.It networks
.Xr getnetbyaddr 3 ,
.Xr getnetbyaddr_r 3 ,
.Xr getnetbyname 3 ,
.Xr getnetbyname_r 3
.It passwd
.Xr getpwent 3 ,
.Xr getpwent_r 3 ,
.Xr getpwnam_r 3 ,
.Xr getpwuid_r 3 ,
.Xr setpwent 3 ,
.Xr endpwent 3
.It shells
.Xr getusershell 3
.It services
.Xr getservent 3
.It rpc
.Xr getrpcbyname 3 ,
.Xr getrpcbynumber 3 ,
.Xr getrpcent 3
.It proto
.Xr getprotobyname 3 ,
.Xr getprotobynumber 3 ,
.Xr getprotoent 3
.It netgroup
.Xr getnetgrent 3 ,
.Xr getnetgrent_r 3 ,
.Xr setnetgrent 3 ,
.Xr endnetgrent 3 ,
.Xr innetgr 3
.El
.Ss Status codes
The following status codes are available:
.Pp
.Bl -tag -width tryagain -compact
.It Sy Status
.Sy Description
.It success
The requested entry was found.
.It notfound
The entry is not present at this source.
.It tryagain
The source is busy, and may respond to retries.
.It unavail
The source is not responding, or entry is corrupt.
.El
.Ss Actions
For each of the status codes, one of two actions is possible:
.Pp
.Bl -tag -width continue -compact
.It Sy Action
.Sy Description
.It continue
Try the next source
.It return
Return with the current result
.El
.Ss Format of file
A BNF description of the syntax of
.Nm
is:
.Pp
.Bl -tag -width <criterion> -compact
.It <entry>
::=
<database> ":" [<source> [<criteria>]]*
.It <criteria>
::=
"[" <criterion>+ "]"
.It <criterion>
::=
<status> "=" <action>
.It <status>
::=
"success" | "notfound" | "unavail" | "tryagain"
.It <action>
::=
"return" | "continue"
.El
.Pp
Each entry starts on a new line in the file.
A
.Sq #
delimits a comment to end of line.
Blank lines are ignored.
A
.Sq \e
at the end of a line escapes the newline, and causes the next line to
be a continuation of the current line.
All entries are case-insensitive.
.Pp
The default criteria is to return on
.Dq success ,
and continue on anything else (i.e,
.Li "[success=return notfound=continue unavail=continue tryagain=continue]" ) .
.Ss Cache
You can enable caching for the particular database by specifying
.Dq cache
in the
.Nm
file.
It should come after
.Dq files ,
but before remote sources like
.Dq nis .
You should also enable caching for this database in
.Xr nscd.conf 5 .
If for a particular query
.Dq cache
source returns success, then no further sources are queried.
On the other hand, if there are no previously cached data, the
query result will be placed into the cache right after
all other sources are processed.
Note that
.Dq cache
requires the
.Xr nscd 8
daemon to be running.
.Ss Compat mode: +/- syntax
In historical multi-source implementations, the
.Sq +
and
.Sq -
characters are used to specify the importing of user password and
group information from NIS .
Although
.Nm
provides alternative methods of accessing distributed sources such as NIS ,
specifying a sole source of
.Dq compat
will provide the historical behaviour.
.Pp
An alternative source for the information accessed via
.Sq +/-
can be used by specifying
.Dq passwd_compat: source .
.Dq source
in this case can be
.Sq dns ,
.Sq nis ,
or
any other source except for
.Sq files
and
.Sq compat .
.Ss Notes
Historically, many of the databases had enumeration functions, often of
the form
.Fn getXXXent .
These made sense when the databases were in local files, but do not make
sense or have lesser relevance when there are possibly multiple sources,
each of an unknown size.
The interfaces are still provided for compatibility, but the source
may not be able to provide complete entries, or duplicate entries may
be retrieved if multiple sources that contain similar information are
specified.
.Pp
To ensure compatibility with previous and current implementations, the
.Dq compat
source must appear alone for a given database.
.Ss Default source lists
If, for any reason,
.Nm
does not exist, or it has missing or corrupt entries,
.Xr nsdispatch 3
will default to an entry of
.Dq files
for the requested database.
Exceptions are:
.Pp
.Bl -tag -width services_compat -compact
.It Sy Database
.Sy "Default source list"
.It group
compat
.It group_compat
nis
.It hosts
files dns
.It passwd
compat
.It passwd_compat
nis
.It services
compat
.It services_compat
nis
.El
.Sh FILES
.Bl -tag -width /etc/nsswitch.conf -compact
.It Pa /etc/nsswitch.conf
The file
.Nm
resides in
.Pa /etc .
.El
.Sh EXAMPLES
To lookup hosts in
.Pa /etc/hosts
, then in cache,
and then from the DNS, and lookup user information from NIS then files, use:
.Pp
.Bl -tag -width passwd: -compact
.It hosts:
files cache dns
.It passwd:
nis [notfound=return] files
.It group:
nis [notfound=return] files
.El
.Pp
The criteria
.Dq [notfound=return]
sets a policy of "if the user is notfound in nis, do not try files."
This treats nis as the authoritative source of information, except
when the server is down.
.Sh NOTES
The
.Nm
file is parsed by each program only once.
Subsequent changes will not be applied until the program
is restarted.
.Pp
If system got compiled with
.Va WITHOUT_NIS
you have to remove
.Sq nis
entries.
.Pp
.Fx Ns 's
.Lb libc
provides stubs for compatibility with NSS modules
written for the GNU C Library
.Nm nsswitch
interface.
However, these stubs only support the use of the
.Dq Li passwd
and
.Dq Li group
databases.
.Sh SEE ALSO
.Xr nsdispatch 3 ,
.Xr nscd.conf 5 ,
.Xr resolv.conf 5 ,
.Xr nscd 8 ,
.Xr ypbind 8
.Sh HISTORY
The
.Nm
file format first appeared in
.Fx 5.0 .
It was imported from the
.Nx
Project, where it appeared first in
.Nx 1.4 .
.Sh AUTHORS
.An Luke Mewburn Aq Mt lukem@netbsd.org
wrote this freely distributable name-service switch implementation,
using ideas from the ULTRIX
.Xr svc.conf 5
and Solaris
.Xr nsswitch.conf 4
manual pages.
